Vibration damped sandwich systems having interlayers of copolymers of vinyl acetate, ethylene and mixtures of isononane-, isodecane- and isoundecane-carboxylic acid vinyl esters

ABSTRACT

Vibration damped sandwich systems having an improved damping effect within a broad range of temperature and consisting of hard plates and a vibration damping interlayer, said interlayer comprising a copolymer of vinyl acetate, ethylene and a mixture of isononane-, isodecane- and isoundecane-carboxylic acid vinyl esters and acrylic and/or methacrylic acid.

United States Patent Oberst et a1.

[451 Feb. 8, 1972 Schommer, Bad Soden,Taunus, all of Germany [73] Assignee: Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt, Main, Germany [22] Filed: Oct. 19, 1970 [21] Appl. No.: 82,174

Related US Application Data [63] Continuation-in-part of Ser. No. 630,962, Apr. 14,

1967, abandoned.

[30] Foreign Application Priority Data Apr. 23, 1966 Germany ..F 49 029 [52] US. Cl ..16l/l65, 261/218, 260/867, 181/33 [51 Int. Cl. ..B32b 7/02, B32b 15/08, E04b 1/99 [58] Field olSearch ..260/86.7;161/165,166,218; 181/33 [56] References Cited UNITED STATES PATENTS 3,256,228 6/1966 Tyran ..117/132 3,386,978 6/1968 Salyer ..260/80.81

Primary Examiner-William J. Van Balen Attorney-Curtis, Morris & Safford [57] ABSTRACT Vibration damped sandwich systems having an improved damping efiect within a broad range of temperature and consisting of hard plates and a vibration damping interlayer, said interlayer comprising a copolymer of vinyl acetate, ethylene and a mixture of isononane-, isodecaneand isoundecane-carboxylic acid vinyl esters and acrylic and/or methacrylic acid.

3 Claims, 4 Drawing Figures PATENTEMEI 0 m2 SHEEY 2 BF 2 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I INVENTORS HERMANN OBERST LEONHARD REIHS JQACHIM EBIGT GUNTHER DUVE ALFRED SCHOMMER ATTORNEYS VIBRATION DAMPED SANDWICH SYSTEMS HAVING INTERLAYFRS OF COPOLYMERS OF VINYL ACETATE, ETIIYLENE AND MIXTURES OF ISONONANE, ISODECANE- AND ISOUNDECANE-CARBOXYLIC ACID VINYL ESTERS This is a continuation-in-part of copending application Ser. No. 630,962 filed Apr. 14, 1967, now abandoned. I

The present invention provides vibration damped sandwich systems having interlayers made of copolymers of vinyl acetate, ethylene and mixtures of isononane-, isodecane-, and

isoundecane-carboxylic acid vinyl esters.

It is known from South African Pat. No. 5,269 that highly valuable vibration damping materials of a broad temperature band suitable for damping bending vibrations of metal sheet constructions can be prepared by a copolymerization of monomers whose homopolymers differ in their second order transition temperature by at least 20 C. This patent also indicates that as vibration damping materials having a broad temperature band there are used, among others, predominantly amorphous copolymers of ethylene and vinyl esters of fatty acids containing two to three carbon atoms, for example vinyl acetate-ethylene copolymers. The vinyl acetate-ethylene copolymers hitherto used, however, have not been able to meet all technical requirements.

It has now been found that sandwich systems of hard plates, in particular metal sheets, having a considerably improved damping efi'ect within a very large temperature range can be obtained by using as a vibration damping self-adhesive interlayer a copolymer of 65 to 30 percent by weight of vinyl acetate, 20 to 40 percent by weight of ethylene, 15 to 30 percent by weight of a mixture of isononane-, isodecaneand isoundecane-carboxylic acid vinyl esters and to 5 percent by weight of acrylic and/or methacrylic acid. The incorporation of a third component still improves the damping properties of vinyl acetate-ethylene copolymers predominantly containing vinyl acetate, and these modified vinyl acetate-ethylene copolymers in which the damping effect depends critically on the weight proportion of the monomers, show straight and extremely broad damping curves having very high maximum values of damping within determined temperature ranges. Moreover, these copolymers may offer the advantage of reducing the costs of a vibration damping material.

, Thus is has, for example, been found that vinyl acetateethylene copolymers modified with to 30 percent by weight of a mixture of isononane-, isodecaneand isoundecane-carboxylic acid vinyl esters are excellent damping materials having a broad temperature band, which can be used at temperatures ranging from l0 to +65 C. The additional incorporation of up to 5 percent by weight of acrylic and/or methacrylic acid still improves the adhesion of the terpolymers to be used according to the invention.

The following example sets forth a satisfactory procedure for preparing copolymers of vinyl acetate, versatic-(9-l1) acid vinyl ester and ethylene. Other known polymerization techniques can also be used to prepare the polymers.

EXAMPLE I A mixture of 1,200 g. of tert. butanol and 50 g. of water was placed into a heatable, 5-1iter, refined-steel, high-pressure autoclave. The pH value of the mixture was adjusted to 4.0 with aqueous hydrochloric acid. The mixture was then heated to 65 C. and an ethylene pressure of 50 atm. was established. A solution of 7.0 g. of azodiisobutyronitrile in a mixture of 300 g. of versatic-(9-l 1) acid vinyl ester and 700 g. of vinyl acetate was added during a period of 3 hours. The reaction temperature and the ethylene pressure was kept constant. Subsequently, the mixture was allowed to react further under the same conditions for 3 hours. The mixture was then cooled, relieved of pressure and the copolymer was isolated from the reaction mixture by removing the solvent and residual monomers under reduced pressure.

The resulting copolymer contained about 20 percent of ethylene, 24 percent of versatic-(9-l l acid vinyl ester and 56 percent of vinyl acetate. The molecular weight was about 750,000.

In the accompanying drawings, FIGS. la and lb are plots showing the loss modulus d as a function of temperature.

A comparison of FIGS. la and lb illustrates the superior efficiency of the novel systems. The curve in FIG. la shows the loss factor d of a metal sheet arrangement of the invention as a function of temperature. It is, for example compared with one of the most effective vibration damping materials known for metal sheet arrangements, namely a modified vinyl acetate copolymer containing plasticizers (curve in FIG. lb). The copolymer shown in the curve of FIG. lb is a thermoplastic adhesive especially suitable for preparing vibration damped metal sheet arrangements comprising two outer metal sheets and a self-adhesive thermoplastic as the vibration damping interlayer. Systems of this type provide a damping effect which is extremely high in its maximum and cannot be exceeded for physical reasons (cf. I'I. Oberst and A. Schommer, Kunststoffe 55, 634, (1965), especially FIG. 9). In a symmetrical arrangement comprising two metal sheets, each of a thickness of 0.5 millimeter, and an interlayer of a thickness of 0.3 millimeter, the loss factor d of the combined system, measured in the bending resonance method (cf. for example I-I. Oberst, L. Bohn and F, Linhardt, Kunststoffe 51, 495 (1961)), almost reaches the value d of l. The known metal sheet constructions damped by one-sided damping coatings which are applied as layers of socalled vibration damping materials capable of being sprayed, trowelled or bonded, show loss factors generally less than d 0.2, the combined system having a technically reasonable thickness of the coating or ratio of coating mass to plate mass. By means of the metal sheet sandwich systems which gain a growing importance in recent times, it is possible to obtain damping values increased by a multiple, when the interlayer material is chosen in the most appropriate composition and thickness, as is shown in the example cited herein.

The temperature bandwidth of the damping in the metal sheet sandwich system does not only depend on the viscoelastic values of the interlayer and of the steel sheets, but, to a considerable extent, also on the geometry of the arrangement, i.e., on the ratio of the layer thicknesses (see cited literature (1965) FIGS. 8 to 10). In the case of metal sheet sandwich systems, it is advantageous to define the band width to be the range of the temperature interval within which the value d 0.05 is exceeded. The damping effect of metal sheets which are not damped by additional vibration damping means in metal sheet constructions of a different kind, corresponds to values d 0.01 and less. The reference value d 0.05 thus means a considerableincrease in the damping effect (by about 15 db. (decibel)) as compared to the nil damping" d 0.01.

In the curve shown in FIG. lb, the reference value d 0.05 is exceeded in the mainly interesting frequency range of from to 1,000 c.p.s. (I-Iz.) at temperatures ranging from about 0 to 50 C., the temperature band width therefore amounts to about 50 C. It is for this reason that sandwich systems of this type are suitable for many technical fields of application. By modifying the content of plasticizers, it is possible to shift the temperature band of a high damping effect to higher temperatures and thus to adapt it to special technical uses, for example in machine units operating at elevated temperatures. This construction mode of metal sheet sandwich systems comprising a self-adhesive interlayer of the most appropriate composition and thickness, of a vibration damping material having a broad temperature band and being prepared by copolymerization of appropriate monomeric components, has hitherto not been excelled by other arrangements of a similar kind and can therefore be regarded as a standard system which can serve for judging the acoustic efficiency of the system of the invention by comparison.

FIGS. la and lb show the temperature curves of the loss factor d of metal sheet sandwich systems comprising steel sheets of a thickness of 0.5 millimeter each and damping interlayers of a thickness of 0.3 millimeter within a frequency range of from 100 to 1,000 c.p.s. The curves have been measured in sandwich systems comprising la) a copolymer of 45 percent by weight of vinyl acetate, 35

percent by weight of ethylene and 20 percent by weight of a mixture of isononane-, isodecaneand isoundecane-carboxylic acid vinyl esters as an interlayer (according to the present invention) and lb) a modified vinyl acetate copolymer containing plasticizers, as an interlayer.

The arrangement 1a) of the invention, whose monomer proportion lies in the optimal range, shows straight curves of the loss factor d in function to temperatures, an excellent temperature bandwidth and high maximum values of damping.

For a temperature bandwidth of 95 C. for 100 c.p.s. (Hz.)

and of 60 C. for l,000 c.p.s. the maximum of damping lies within a temperature range of from to 25 C., as to low temperatures, the application range reached down to a temperature of l0 C. Due to its broader temperature band, the interlayer material of arrangement 1a) is superior to that of arrangement lb); it can therefore be used for correspondingly more purposes.

A particular advantage of this vibration damping material resides in the fact that it is perfectly suitable for being applied continuously in the mass production of sandwich metal sheets. I

It also is a thermoplastic adhesive which can be applied to the metal sheets by trowelling, brushing or pouring at elevated temperatures. The sandwich system is then advantageously cooled under pressure between rolls. Except for degreasing the metal sheets do neither require a preliminary treatment nor another bond. Copolymers containing acrylic or methacrylic acid groups may even do without degreasing. An excellent adhesion is achieved.

The vibration damping material has a good resistance to flow within the range of the application temperatures, a resistance which may still be improved in the copolymers containing carboxyl groups, by a slight cross-linking, for example with epoxides or isocyanates. The sandwich metal sheets can be processed in a manner corresponding, within wide limits, to that of usual metal sheets, i.e., they may be creased, bent, shaped, welded and riveted. Unless their curvature radii are too narrow, they may even be formed with plug and ring. There are obtained sandwich metal sheets of general use, having such a high damping effect and such a broad temperature range of damping as are well sufficient for numerous fields of application.

Small amounts of fillers, for example for improving the electric conductivity (improvement of the resistance welding) may be added to the vibration damping material. For not adversely affecting the damping effect, it is advantageous to add less than 1 percent by weight, preferably less than 0.5 percent by weight calculated on the polymer, of the filler amount. Appropriate fillers are, for example, heavy spar, silicic acid, graphite and soot.

The total thickness of the sandwich system of the invention preferably ranges between 1 to 6 millimeters. The interlayers may be in the range of from 0.1 to l millimeter, preferably from 0.2 to 0.5 millimeter. The maximum damping effect is obtained in symmetrical sandwich systems. The stifi ness in flexure and the stability, however, are higher in asymmetric sandwich arrangements having the same weight. These asymmetric sandwich systems are therefore preferred for uses which require the highest possible stability, calculated on the weight. The ratio between the thicknesses of, for example metal sheets, preferably ranges between [:1 and 1:4.

FIG. 2a shows a sandwich system of the invention in a symmetrical arrangement.

FIG. 2b shows a sandwich system in an asymmetric arrangement. The two outer plates or sheets (1) have the vibration damping layer (2) therebetween.

What is claimed is: l. A vibration damped sandwich system of hard plates and a vibration damping interlayer having a considerably improved damping effect with a very large temperature range, the material of said interlayer comprising a terpolymer of 65 to 30 percent by weight of vinyl acetate, 20 to 40 percent by weight of ethylene, and 15 to 30 percent by weight of a mixture of isononane-, isodecane and isoundecane-carboxylic acid vinyl ester.

2. A vibration damped sandwich system as claimed in claim 1, wherein the copolymer of the interlayer contains up to 1 percent by weight, calculated on the terpolymer of a tiller.

3. A vibration damped sandwich system as claimed in claim 1 wherein the plates have a thickness radio therebetween in the range offrom 1:1 to 1:4.

* w s z 

2. A vibration damped sandwich system as claimed in claim 1, wherein the copolymer of the interlayer contains up to 1 percent by weight, calculated on the terpolymer of a filler.
 3. A vibration damped sandwich system as claimed in claim 1 wherein the plates have a thickness ratio therebetween in the range of from 1:1 to 1:4. 